Research firm Gartner reported a dip in global sales of mobile phones for the second quarter in a row and will likely cut its 2012 outlook as consumers hold back on handset upgrades due to economic uncertainty.

The research group, whose data is widely used in the mobile sector, also said handset maker Samsung extended its lead over Apple and grew its market share to more than one fifth in the second quarter of 2012.

"For 2012, the overall market is looking weaker than what I had actually forecast at the start of the year," said Anshul Gupta, principal research analyst at Gartner, which previously expected 2012 mobile phone sales of around 1.9 billion units.

"Consumers are really holding on to their old devices," he said.

Mobile phone sales fell 2 percent in the second quarter from a year earlier to 419 million units, Gartner said.

While some were waiting for new, high-profile devices like Apple's iPhone 5 due later in the year, many others were simply postponing expensive purchases or waiting for promotions, Gupta said.

Despite the overall weakness, Samsung's quarterly mobile phone sales rose around 30 percent from a year earlier, helped by record sales of Galaxy smartphones.

It overtook Nokia as the leading mobile phone maker with a 22 percent share of the overall market, the report

showed.

Nokia's mobile phone sales fell 15 percent, and its share fell to 20 percent from 23 percent a year earlier.

By operating system, Google's Android extended its lead with 64 percent market share compared with 43 percent a year earlier, while Apple iOS held a 19 percent share, little changed from a year earlier.

Nokia's old Symbian system tumbled to 6 percent from 22 percent but Microsoft Windows, which the Finnish mobile phone maker now uses, rose to nearly 3 percent from under 2 percent a year ago.